Method and system for engine control

ABSTRACT

Methods and systems are provided for restarting an engine when a high pressure fuel pump is degraded. In response to an indication of high pressure fuel pump degradation, fuel may be injected during an intake stroke, rather than a compression stroke, for a selected number of combustion events since the engine restart. By shifting to an intake stroke injection, the engine may be started even when sufficient fuel rail pressures are not available.

TECHNICAL FIELD

The present application relates to methods and system for operating anengine with a high pressure fuel pump.

BACKGROUND AND SUMMARY

Direct injection fuel systems may be used to deliver at least a portionof a desired amount of fuel to an engine for combustion. Such directinjection fuel systems may include a high pressure fuel pump, inaddition to a low pressure fuel pump, upstream of a fuel rail to raise apressure of the fuel delivered to the engine cylinders through thedirect injectors. In vehicle start/stop systems configured to perform anidle-stop when idle-stop conditions are met and automatically restartthe engine when restart conditions are met, the high pressure pump mayalso be used to compression inject fuel into one or more cylinders andrestart the engine. In particular, during engine restart conditions, thehigh pressure pump may be used to provide sufficient injector pressureto force fuel into the selected cylinders during a compression stroke,thereby reducing engine restart times as well as restart engine speedflares.

However, the inventors herein have identified potential issues with suchsystems. As one example, during conditions when the high pressure fuelpump is degraded, the fuel rail pressure may be reduced to a lower levelcorresponding at least to the low pressure fuel pump. If the highpressure pump is degraded at the time of engine restart, the reducedpressure level may not be sufficient to force the fuel into the cylinderduring the compression stroke. As a result, no combustion may occurduring cranking and the starter may fault. If the high pressure pumpdegrades during the run up (e.g., after the first or second combustionevent during the run up), an engine stall may occur. Engine misfireevents may also be possible. As such, the overall engine restartresponse may be degraded. The effects may be exacerbated in vehiclestart/stop systems due to the higher frequency of engine restarts fromidle-stop conditions.

Thus at least some of the above issues may be addressed by a method ofoperating an engine comprising, during an engine cold start condition,direct injecting fuel into a first firing cylinder during an intakestroke independent of a state of a high pressure fuel pump coupled tothe engine to restart the engine. In this way, engine startability canbe improved even if the high pressure fuel pump is degraded.

In one example, during an engine restart, it may be determined if a highpressure fuel pump is degraded. If so, fuel may be injected into thefirst firing cylinder (e.g., the first cylinder to reach TDC after theengine starts to rotate) during the intake stroke. For example, the fuelinjection may be shifted from multiple injections in the compressionstroke to a single injection in the intake stroke. Optionally, directfuel injection during the intake stroke may be maintained for a numberof combustion events since the engine start. In one example, the intakestroke injection may be maintained until a threshold engine speed isreached (e.g., until an idling speed is reached). While direct injectingduring the intake stroke, a spark timing may be retarded. However, alower amount of spark retard may be applied for the intake strokeinjection relative to a corresponding compression stroke injection, toreduce the engine speed flare while providing combustion torque.Likewise, while direct injecting during the intake stroke, a smalleralternator load may be applied on the engine relative to thecorresponding compression stroke injection, to reduce restart NVH issuesand improve vehicle launch smoothness. Still other throttle, valvetiming, transmission gear, etc. adjustments may be performed incoordination with the intake stroke injection to improve engine restartin the presence of a degraded high pressure fuel pump.

In this way, by injecting fuel in the intake stroke during an enginerestart, in response to an indication of high pressure pump failure,sufficient injector pressure may be developed to force fuel into thefirst firing cylinder. As such, this improves engine restartability andreduces the likelihood of engine stalls and misfires. By adjusting oneor more engine parameters while injecting the fuel during an intakestroke, engine speed flares and NVH issues associated with an enginerestart can also be addressed. Overall, an engine may be restarted evenif a high pressure pump is degraded.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example engine system.

FIG. 2 shows a schematic depiction of an example engine system that maybe selectively deactivated in response to idle-stop conditions.

FIG. 3 shows a schematic depiction of a fuel system including a highpressure fuel pump coupled to the engine system of FIGS. 1 and 2.

FIG. 4 shows a high level flow chart for adjusting fuel injection to anengine cylinder during an engine cold start based on a state of the highpressure fuel pump.

FIG. 5 shows a high level flow chart for adjusting engine idle-stop andrestart operations responsive to an indication of high pressure fuelpump degradation.

FIG. 6 shows an example fuel injection adjustment responsive to anindication of high pressure fuel pump degradation.

DETAILED DESCRIPTION

Methods and systems are provided for adjusting engine operations in anengine system (such as the engine systems of FIGS. 1 and 2) configuredto receive fuel via a high pressure fuel pump (such as the fuel systemof FIG. 3). An engine controller may be configured to adjust engineoperations during an engine restart based on whether the high pressurefuel pump (HPP) is functional or degraded. The controller may beconfigured to perform a control routine, such as the routine depicted inFIG. 4, during an engine cold start, to inject fuel into the firstfiring cylinder in the intake stroke, and then either maintain the fuelinjection in the intake stroke for at least an additional number ofcombustion events (such as, in response to a degraded HPP) or shiftinjection to the compression stroke (such as, in response to afunctional HPP). The controller may also be configured to perform acontrol routine, such as the routine depicted in FIG. 5, during anengine restart from idle-stop conditions, to perform a single intakestroke fuel injection (such as, in response to a degraded HPP) orperform a multiple compression stroke fuel injection (such as, inresponse to a functional HPP). An example fuel injection adjustment isshown in FIG. 6. Based on which stroke the fuel injection is made in,engine operating parameters, such as throttle opening, valve timing,spark timing, alternator load, etc., may also be adjusted during therestart. By shifting fuel injection from a compression stroke to anintake stroke during an engine restart, in response to an indication ofhigh pressure pump degradation, sufficient injector pressure may bedeveloped to force fuel into the first firing cylinder, improving enginestartability.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (hereinalso “combustion chamber”) 14 of engine 10 may include combustionchamber walls 136 with piston 138 positioned therein. Piston 138 may becoupled to crankshaft 140 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 140 maybe coupled to at least one drive wheel of the passenger vehicle via atransmission system. Further, a starter motor (not shown) may be coupledto crankshaft 140 via a flywheel to enable a starting operation ofengine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 14 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a high pressure fuel system 8 including fueltanks, fuel pumps, and a fuel rail. One example of such a fuel system isshown in FIG. 3.

It will be appreciated that, in an alternate embodiment, injector 166may be arranged in intake passage 146, rather than in cylinder 14, in aconfiguration that provides what is known as port injection of fuel(hereafter referred to as “PFI”) into the intake port upstream ofcylinder 14.

In one embodiment, cylinder 14 may include only a single fuel injectorthat is configured to receive different fuels from the fuel system invarying relative amounts as a fuel mixture, and is further configured toinject this fuel mixture either directly into the cylinder as a directfuel injector or upstream of the intake valves as a port fuel injector.In alternate embodiments, the engine may be operated by using twoinjectors (a direct injector and a port injector) and varying a relativeamount of injection from each injector.

Fuel may be delivered by injector 166 to cylinder 14 during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel delivered from the injector may vary with operating conditions,such as aircharge temperature, as described herein below. Furthermore,for a single combustion event, multiple injections of the delivered fuelmay be performed per cycle. The multiple injections may be performedduring the compression stroke, intake stroke, or any appropriatecombination thereof.

As an example, during an engine restart, fuel may be injected into acylinder during a compression stroke. By performing compression directfuel injection, a higher air-charge temperature and higher valvetemperature of the engine cylinders during the compression stroke may beadvantageously used to more effectively evaporate the directly injectedfuel. In particular, for fuels with a relatively low volatility (such asalcohol fuels), the compression stroke injection may allow the fuel tobe exposed to higher air-charge temperatures, thereby better enablingefficient evaporation and formation of a homogenous air-fuel mixture. Assuch, this improves the startability of the engine.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc. It will beappreciated that engine 10 may include any suitable number of cylinders,including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each ofthese cylinders can include some or all of the various componentsdescribed and depicted by FIG. 1 with reference to cylinder 14.

Fuel tanks in fuel system 8 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In one example, fuels with different alcohol contents could include onefuel being gasoline and the other being ethanol or methanol. In anotherexample, the engine may use gasoline as a first substance and an alcoholcontaining fuel blend such as E85 (which is approximately 85% ethanoland 15% gasoline) or M85 (which is approximately 85% methanol and 15%gasoline) as a second substance. Other alcohol containing fuels could bea mixture of alcohol and water, a mixture of alcohol, water and gasolineetc. In still another example, both fuels may be alcohol blends whereinthe first fuel may be a gasoline alcohol blend with a lower ratio ofalcohol than a gasoline alcohol blend of a second fuel with a greaterratio of alcohol, such as E10 (which is approximately 10% ethanol) as afirst fuel and E85 (which is approximately 85% ethanol) as a secondfuel. Additionally, the first and second fuels may also differ in otherfuel qualities such as a difference in temperature, viscosity, octanenumber, latent enthalpy of vaporization etc.

Moreover, fuel characteristics of the fuel tank may vary frequently. Inone example, a driver may refill the fuel tank with E85 one day, and E10the next, and E50 the next. The day to day variations in tank refillingcan thus result in frequently varying fuel compositions, therebyaffecting the fuel composition delivered by injector 166.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

FIG. 2 shows a block diagram layout of a vehicle system 210, including avehicle drive-train 220. Drive-train 220 may be powered by engine 222.Engine 224 may be configured to receive fuel from fuel system 8including various fuel tanks, pumps, and valves, as elaborated withreference to FIG. 3. Engine 224 may be configured to operate on one ormore fuels such as gasoline, ethanol, combinations thereof, diesel, etc.Engine 224 may be started with an engine starting system 225, includinga starter. In one example, the starter may include an electrical motor.The starter may be configured to support engine restart at or below apredetermined near zero threshold speed, for example at or below 50 rpm,or 100 rpm. Torque of engine 224 may be adjusted via torque actuator226, such as a fuel injector, throttle, etc. Additionally, in the caseof a hybrid vehicle, the powertrain may be used to slow or increaseengine speed as desired.

An engine output torque may be transmitted to torque converter 228 todrive an automatic transmission 230. In some examples, the torqueconverter may be referred to as a component of the transmission. Theoutput of the torque converter 228 may be controlled by torque converterlock-up clutch 234. When torque converter lock-up clutch 234 is fullydisengaged, torque converter 228 transmits torque to automatictransmission 230 via fluid transfer between the torque converter turbineand torque converter impeller, thereby enabling torque multiplication.In contrast, when torque converter lock-up clutch 234 is fully engaged,the engine output torque is directly transferred via the torqueconverter 228 clutch to an input shaft (not shown) of transmission 230.Alternatively, the torque converter lock-up clutch 234 may be partiallyengaged, thereby enabling the amount of torque relayed to thetransmission to be adjusted.

Torque output from the automatic transmission 230 may in turn be relayedto wheels 236 to propel the vehicle. Specifically, automatictransmission 230 may adjust an input driving torque at the input shaft(not shown) responsive to a vehicle traveling condition beforetransmitting an output driving torque to the wheels. For example,transmission torque may be transferred to vehicle wheels 236 by engagingone or more clutches, including forward clutch 232. As such, a pluralityof such transmission clutches may be engaged, as needed. Further, wheels236 may be locked by engaging wheel brakes 238. In one example, wheelbrakes 238 may be engaged in response to the driver pressing his foot ona brake pedal (not shown). In the same way, wheels 236 may be unlockedby disengaging wheel brakes 238 in response to the driver releasing hisfoot from the brake pedal.

Vehicle system components outside of the drivetrain may include analternator 242, and a battery 246. Additional auxiliary loads (notshown) may include lights, radio system, HVAC systems (for heatingand/or cooling a vehicle cabin), etc. Alternator 242 may be configuredto convert the mechanical energy generated while running engine 224 toelectrical energy for storage in battery 246. Alternator 242 may includea field coil (not shown). As such, when a current is applied to thealternator field coil 242, the coil is energized, and accordingly a loadis applied on the engine 224. The rotating engine 224, mechanicallycoupled to the alternator, causes current to flow in the stator ofalternator 242.

In one example, as depicted, engine 224 may be configured to beselectively (and automatically) shut down when idle-stop conditions aremet and restarted when restart conditions are met. One or more auxiliaryloads may be maintained, for example, at 12V, even when the engine isoff The power to maintain the auxiliary loads operational when theengine is shut down may be provided, at least in part, by battery 246,one or more additional batteries (e.g., one or more additional smallerbatteries), and/or a DC/DC converter (not shown). In one example, aDC/DC converter based device, such as a voltage quality module (VQM) ora voltage stability module (VSM) (not shown) may be electrically coupledbetween battery 246 and alternator 242 and may be configured to providea regulated DC voltage output from a DC voltage input (or power source),such as battery 246. The output of the DC/DC converter may be applied tothe various auxiliary loads including the alternator field coil circuit.

As elaborated in FIGS. 4-5, during an engine restart, an alternator loadmay be applied on the engine, for example, by adjusting a currentapplied to the alternator field coil. Controller 240 may be configuredto receive inputs from engine 224 and accordingly adjust a mechanicalload applied to the engine via the alternator by adjusting a currentsupplied to the alternator field coil. As one example, an engine startspeed profile may be selected, and the controller may adjust a currentsupplied to the alternator field coil based on a difference betweenactual engine speed and a desired engine speed profile. In this way, itis possible to adjust a load applied to an engine via an alternatormechanically coupled to the engine during engine starting so that enginespeed can be controlled to a desired engine speed.

Controller 240 may also adjust an engine torque output by adjusting acombination of spark timing, fuel pulse width, fuel pulse timing, and/orair charge, by controlling throttle opening and/or valve timing, valvelift and boost for turbo- or super-charged engines. In the case of adiesel engine, controller 240 may control the engine torque output bycontrolling a combination of fuel pulse width, fuel pulse timing, andair charge. In all cases, engine control may be performed on acylinder-by-cylinder basis to control the engine torque output.

When idle-stop conditions are satisfied (e.g., when the vehicle isidling and engine operating parameters are within a desired range),controller 240 may selectively shut down the engine, for example, bycontrolling operation of drivetrain and/or accessory components. Aselaborated in FIG. 5, the controller may maintain one or moretransmission clutches engaged or disengaged during the engine shutdown,based on a state of a high pressure fuel pump coupled to the fuel system8 of engine 224. Similarly, when engine restart conditions are met, suchas when the vehicle is already in an idle-stop and one or more engineoperating parameters are outside the desired range, controller 240 mayselectively restart the engine by powering the starter using a battery.As elaborated in FIG. 5, the controller may maintain one or moretransmission clutches engaged or disengaged during the engine restart,based on a state of a high pressure fuel pump coupled to the fuel system8 of engine 224. Further, controller 240 may use engine torque actuatorsalong with making adjustments to current supplied to an alternator fieldcoil to control engine speed during engine starting. By controllingengine torque actuators and the load applied to the engine via thealternator it may be possible to reduce engine speed flares duringengine starting.

FIG. 3 shows a schematic depiction of a fuel system 300 configured todeliver fuel to an internal combustion engine that utilizes directinjection (DI) for use in a vehicle. In one example, fuel system 300 isan example embodiment of fuel system 8 of FIGS. 1-2. Fuel system 300 mayinclude each of a first, high pressure fuel pump (HPP) and a lowpressure fuel pump (LPP) to deliver fuel to the engine 324.Specifically, fuel system 300 includes low-pressure fuel pump 302 topump liquid fuel from fuel tank 308. In this embodiment, fuel pump 302is an electronically controlled variable speed lift pump. In some cases,low-pressure fuel pump 302 may only operate at a limited number ofspeeds. It will be appreciated that the fuel tank may contain any fuelsuitable for an internal combustion engine such as gasoline, methanol,ethanol, or any combination thereof.

Low-pressure fuel pump 302 is fluidly coupled to check valve 304 tofacilitate fuel delivery and maintain fuel line pressure. In particular,check valve 304 includes a ball and spring mechanism that seats andseals at a specified pressure differential to deliver fuel downstream.In some embodiments, fuel delivery system 300 may include a series ofcheck valves fluidly coupled to low-pressure fuel pump (LPP) 302 tofurther impede fuel from leaking back upstream of the valves. Checkvalve 304 is fluidly coupled to filter 306. Filter 306 may remove smallimpurities that may be contained in the fuel that could potentiallydamage vital engine components.

Fuel may be delivered from filter 306 to high-pressure fuel pump 310.High pressure fuel pump 310 may increase the pressure of fuel receivedfrom the fuel filter from a first pressure level generated bylow-pressure fuel pump 302 to a second pressure level higher than thefirst level. High pressure fuel pump 310 may deliver high pressure fuelto fuel rail 318 via fuel line 314. In one example, high pressure fuelpump is a volumetric displacement fuel pump.

Fuel pressure regulator 312 may be coupled in line with fuel line 314 toregulate fuel delivered to fuel rail 318 at a set-point pressure. Toregulate the fuel pressure at the set-point, fuel pressure regulator 312may return excess fuel to fuel tank 308 via return line 316. It will beappreciated that operation of fuel pressure regulator 312 may beadjusted to change the fuel pressure set-point to accommodate operatingconditions.

Fuel rail 318 may distribute fuel to each of a plurality of fuelinjectors 320. Each of the plurality of fuel injectors 320 may bepositioned in a corresponding cylinder 322 of engine 324 such thatduring operation of fuel injectors 320 fuel is injected directly intoeach corresponding cylinder 322. Alternatively (or in addition), engine224 may include one or more port fuel injectors positioned at the intakeport of each cylinder such that during operation of the fuel injectorsfuel is port injected in to the intake port of each cylinder. In, theillustrated embodiment, engine 224 includes four cylinders. However, itwill be appreciated that the engine may include a different number ofcylinders.

As previously elaborated, during an engine restart (such as an enginerestart from idle-stop conditions), fuel may be injected into a cylinderduring a compression stroke. To enable direct injection of fuel into thecylinder during a compression stroke, a fuel rail pressure may be raisedby operating the high pressure fuel pump. During conditions when highpressure fuel pump 310 is degraded, the fuel rail pressure may drop tothe level of the low pressure fuel pump (e.g., from 500-700 psi to 50-60psi). The high pressure fuel pump may be degraded due to, for example,an electrical fault. One common high pressure fuel pump electrical faultmay include shorting to ground that causes the high pressure pump'selectric circuit to fault and the rail pressure to go to the lowpressure fuel pump circuit's pressure. As another example, the highpressure fuel pump may be degraded due to a leak in a high pressureregulator. As such, if the leak is small enough, a low pressureregulator may compensate. However, if the leak is too large, there maynot be sufficient fuel pressure in the rail (e.g., no fuel railpressure). The high pressure pump may be mechanically driven off anengine cam, wherein the number of cam lobes is engine specific. Forexample, on an I4 engine, there may be 1 lobe/cylinder, while on a V6engine, there may be 1 lobe/2 cylinders. In either case, there is anelectronically controlled valve that controls the flow through the highpressure pump. High pressure pump degradation may also be caused if thisvalve fails to actuate. In particular, if the valve fails to actuate,the fuel rail pressure of the high pressure pump may typically go to thelow pressure pump output of ˜50-60 psi.

At the low pressure level resulting from high pressure fuel pumpdegradation, there may not be sufficient injector pressure to force fuelinto the cylinder during a compression stroke. That is, compressionstroke injection may not be possible. When this occurs during an enginerestart, no combustion may occur and the engine will crank until thestarter degrades. Likewise, if the high pressure fuel pump degradationoccurs after the first or second combustion event (since the enginerestart), during engine run-up, an engine stall may occur. In addition,when the fuel rail pressure drops to the low pressure fuel pump outletpressure, fuel atomization, vaporization, and/or charge preparation candegrade. Overall, engine startability is degraded.

As elaborated with reference to FIGS. 4-5, if the high pressure fuelpump is degraded, an engine controller may be configured to shift fuelinjection into a first firing cylinder (and/or a selected number ofcombustion events since an engine restart) from the compression stroketo an intake stroke. By performing intake stroke direct fuel injectionfor at least the first firing cylinder (and/or the selected number ofcombustion events since the engine restart), the likelihood of asuccessful engine restart, while a high pressure fuel pump is degraded,can be increased. By resuming compression injection after intake strokeinjection into the first firing cylinder (and/or the selected number ofcombustion events since the engine restart), the higher air-chargetemperature and higher valve temperature of the engine cylinders duringthe compression stroke may be advantageously used to more effectivelyevaporate the directly injected fuel. In particular, for fuels with arelatively low volatility (such as alcohol fuels), the subsequentcompression stroke injection may allow the fuel to be exposed to higherair-charge temperatures, thereby better enabling efficient evaporationand formation of a homogenous air-fuel mixture. As also elaborated inFIGS. 4-5, intake stroke direct fuel injection may be used for the firstfiring cylinder during an engine cold start irrespective of the state ofthe high pressure fuel pump. Subsequently, intake stroke injection maybe continued for a selected number of combustion events since the enginerestart if the high pressure fuel pump is degraded. Alternatively,compression stroke injection may be resumed for the selected number ofcombustion events since the engine restart if the high pressure fuelpump is not degraded. Herein, most of the injected fuel may be betterevaporated, less fuel may be lost during engine operation, and the needfor larger or pilot fuel injections at an engine cold-start may bereduced. This may provide fuel economy benefits as well as reducedcold-start exhaust emissions.

Returning to FIG. 3, controller 332 may receive various signals fromsensors coupled to fuel system 300 and engine 324. For example,controller 332 may receive a fuel pressure (and/or temperature) signalfrom fuel sensor 326 which may be positioned downstream of high-pressurefuel pump 310 (e.g. positioned in fuel line 314). In some cases, fuelpressure measured by fuel sensor 326 may be indicative of fuel railpressure. In some embodiments, a fuel sensor may be positioned upstreamfrom high-pressure fuel pump 310 to measure a pressure of fuel exitinglow-pressure fuel pump 302. Further, controller 332 may receiveengine/exhaust parameter signals from engine sensor(s) 328. For example,these signals may include measurement of inducted mass air flow, enginecoolant temperature, engine speed, throttle position, and absolutemanifold pressure, emission control device temperature, etc. Note thatvarious combinations of the above measurements as well as measurementsof other related parameters may be sensed by sensor(s) 328.

Controller 332 may provide feedback control based on signals receivedfrom the various fuel sensors 326, and engine sensor(s) 328. Forexample, controller 332 may send signals to adjust a current level orpulse width of a mechanical solenoid valve (MSV) of high-pressure fuelpump 310 to adjust operation of high-pressure fuel pump 310, a fuelpressure set-point of fuel pressure regulator 310, and/or a fuelinjection amount and/or timing based on signals from fuel sensor 326,and engine sensor(s) 328.

In one example controller 332 is a microcomputer that includes amicroprocessor unit, input/output ports, an electronic storage mediumfor executable programs and calibration values such as read only memory,random access memory, keep alive memory, and a data bus. The storagemedium read-only memory can be programmed with computer readable datarepresenting instructions executable by the processor for performing themethod described below as well as other variants that are anticipatedbut not specifically listed.

Controller 332 can also control the operation of each of fuel pumps 302and 310 to adjust an amount, pressure, flow rate, etc., of a fueldelivered to the engine. As one example, controller 332 can vary apressure setting and/or fuel flow rate of the fuel pumps to deliver fuelto different locations of the fuel system. In one example, where thehigh pressure fuel pump is a volumetric displacement fuel pump, thecontroller may adjust a flow control valve of the high pressure pump tovary the effective pump volume of each pump stroke.

In this way, the components of FIGS. 1-3 enable a method of operating anengine wherein during an engine cold start condition, fuel may be directinjected into a first firing cylinder during an intake strokeindependent of a state of the high pressure fuel pump coupled to theengine to restart the engine. In this way, sufficient pressure may begenerated to crank the engine, thereby improving engine startability.

Now turning to FIG. 4, an example routine 400 is shown for adjustingengine operations, including fuel injection, during an engine coldstart, based on whether or not a high pressure fuel pump of the fuelsystem is degraded.

At 402, engine operating conditions may be estimated and/or measured.These may include, for example, torque demand, engine temperature,exhaust catalyst temperature, desired boost level, etc. Next at 404, itmay be determined if engine cold start conditions are confirmed. In oneexample, an engine cold start condition may be determined uponconfirmation of one or more of an exhaust catalyst temperature beingbelow a threshold temperature, and the engine being in an engine-offcondition for greater than a threshold time.

If engine cold-start conditions are confirmed, then at 406, the routineincludes, during the engine cold start condition, direct injecting fuelinto a first firing cylinder during an intake stroke independent of astate of a high pressure fuel pump coupled to the engine system. Thatis, fuel may be direct injected into the first firing cylinder duringthe intake stroke if the high pressure fuel pump is not degraded, andfuel may be direct injected into the first firing cylinder during theintake stroke if the high pressure fuel pump is degraded. As usedherein, the intake stroke injection may include injecting fuel as asingle injection during the intake stroke. As such, the first firingcylinder may be selected based on piston position. For example, thefirst firing cylinder may be a first cylinder that reaches TDC after theengine begins to rotate. By injecting in the intake stroke irrespectiveof the state of the high pressure fuel pump, fuel vaporization andair-fuel mixing can be improved to reduce exhaust emissions before theexhaust catalyst is active (e.g., at or above the catalyst light-offtemperature).

Next, at 408, it may be determined if the high pressure fuel pump (HPP)is degraded. In one example, high pressure pump degradation may havebeen identified during a preceding engine cycle (e.g., immediatelypreceding cycle) by performing appropriate diagnostic routines. As such,if the high pressure pump is degraded, compression stroke fuel injectionmay not be performed efficiently. Specifically, the reduced pressurelevel in the fuel line may not be sufficient to force fuel into acylinder during a compression stroke. Thus, based on whether or not thehigh pressure fuel pump is degraded, the routine may include eithercontinuing direct injecting fuel in the intake stroke during therestart, or shifting to the compression stroke, for a number ofcombustion events since the engine restart.

Specifically, if the high pressure fuel pump is not degraded, then at410, the routine includes resuming compression injection of fuel duringthe restart. Therein, fuel may be direct injected in the compressionstroke as multiple injections (herein, also referred to as a splitinjection). By injecting fuel in the compression stroke, the higherair-charge temperature and higher valve temperature of the enginecylinders during the compression stroke may be advantageously used tomore effectively evaporate the directly injected fuel. By enablingefficient evaporation and formation of a homogenous air-fuel mixture,engine startability can be enhanced. At 412, one or more engineoperating parameters may be adjusted based on the compression strokeinjection to reduce an engine restart speed flare. These may include,for example, a spark ignition timing, an alternator load, a throttleposition, a valve timing, a cam timing, etc. The various engineoperating parameters may be adjusted to reduce an engine restart speedflare, to reduce NVH issues, and improve smoothness of vehicle launch inengine configured to perform idle-stops. For example, spark timing maybe retarded by a larger amount (e.g., by −25 to −30 if late compressioninjection is used vs. −10 to −15 CA deg if intake injection is used). Assuch, a larger amount of spark retard may be tolerated when fuel isinjected in the compression stroke relative to the intake stroke. Asanother example, a larger alternator load may be applied on the engineuntil a threshold engine speed is reached (such as an engine idlingspeed). As yet another example, the throttle may be at least partiallyopened (or maintained more open) until the threshold speed is reachedduring the engine restart. Still other adjustments to valve timing, camtiming, etc. may be performed.

In one example, the compression stroke injections may be continued atleast until a threshold speed (e.g., an engine idling speed) is reached.Accordingly, at 418, it may be confirmed if the threshold engine speedhas been reached. Upon confirming that the threshold engine speed hasbeen reached, at 420, the routine may transition to a fuel injectiontiming that is based at least on engine speed and load conditions.

Returning to 408, if the high pressure fuel pump is degraded, then at414, the routine includes continuing to direct inject fuel during theintake stroke for a number of combustion events since the enginerestart. Therein, fuel may continue to be injected in the intake strokeas a single fuel injection. By continuing to inject fuel in the intakestroke, the engine restart speed flare may be better addressed in theabsence of the high pressure fuel pump. The number of combustion eventsover which the intake stroke injection is continued may be based on theindication of high pressure fuel pump degradation. For example, inresponse to the indication of degradation, intake stroke combustion maybe continued beyond the first firing cylinder, and into the first fourfiring cylinders. As another example, the number of combustion eventsover which the intake stroke injection is continued may be further basedon the engine cylinder configuration. For example, intake strokecombustion may be continued beyond the first firing cylinder, and intothe first four firing cylinders, for a four-cylinder engine, but intothe first six cylinders for a six-cylinder engine, and so on. In stillanother example, the number of combustion events may be based on anengine speed such that the direct injecting in the intake stroke iscontinued for a number of combustion events until an engine speed is ator above a threshold speed (such as, an engine idling speed).

Next, at 416, one or more engine operating parameters may be adjustedbased on the intake stroke injection to assist in reducing an enginerestart speed flare. For example, while direct injecting fuel during theintake stroke, an ignition spark timing may be adjusted based on thedirect injection. Since a larger amount of spark retard is possible witha compression stroke injection relative to an intake stroke injection,herein, spark timing may be retarded by a smaller amount while directinjecting in the intake stroke. As another example, while directinjecting fuel during the intake stroke, the controller may apply analternator load on the engine, the alternator load based on one or moreof combustion event number, and speed profile (e.g., desired speedprofile and/or desired acceleration profile). Specifically, a smalleralternator load may be applied on the engine (relative to the largeralternator load applied during the compression stroke injection) until athreshold engine speed is reached (such as an engine idling speed). Asyet another example, the throttle may be maintained closed (or less openrelative to the throttle opening used during a compression strokeinjection) until the threshold speed is reached during the enginerestart. Still other adjustments to valve timing, cam timing, etc. maybe performed. In one example, an intake and/or exhaust valve timing ofthe first firing cylinder (at 406) as well as the subsequent firingcylinders undergoing intake stroke injection, may be adjusted so thatthe intake stroke direct fuel injection occurs during positive valveoverlap. By injecting the fuel during positive valve overlap, furtherimprovements in air-fuel mixing may be achieved.

For example, in engines configured to be selectively shutdown inresponse to engine idle-stop conditions, and restarted in response toengine restart conditions, a base CAM timing may be typically set tohave minimal positive overlap and a small amount of negative overlap(e.g., 8 CA deg of negative overlap). The small amount of negativeoverlap may reduce the potential for exhaust gasses, (that is,residuals) from flowing into the intake manifold during an engineshutdown. Cam timing adjustments may also be a function of the intakemanifold pressure near the end of shutdown. Thus, as the engine speedapproaches zero, the throttle may be held closed from the beginning ofshutdown. As an example, the throttle may be opened as a function ofengine speed, e.g. at 300 RPM, during shutdown to reduce the exhaust gastransfer. As such, positive valve overlap may provide further advantagesduring cold start for engines that run on alcohol fuels, such as onE85-E100 fuels. For example, in engines configured with idle-stop, ifthe engine is “warmed-up”, engine stability with E85 as a fuel may beimproved. The intake stroke injection and accompanying engine operatingparameter adjustments (e.g., adjustments to spark retard, alternatorload, valve timing, throttle position, etc.) may be maintained for anumber of combustion events until a threshold engine speed is reached.For example, until an engine idling speed is attained. At 418 it may beconfirmed if the threshold engine speed has been reached. Uponconfirming that the threshold engine speed has been reached, at 420, theroutine may transition to a fuel injection timing that is based at leaston engine speed and load conditions.

In this way, by injecting fuel into a first firing cylinder during anintake stroke, when performing an engine cold start, fuel vaporizationand air-fuel mixing can be improved to reduce exhaust emissions beforethe exhaust catalyst is activated (e.g., at or above the catalystlight-off temperature). As such, substantial air-fuel mixing may berequired when the engine is spinning relatively slowly (such as when anengine restart is initiated). Thus, by injecting fuel in the intakestroke, more time is allowed for the fuel to vaporize, and for the aircharge to mix with the fuel. By performing intake stroke injections whena high pressure fuel pump is degraded, air-fuel mixing and fuelatomization can be enabled even at relatively lower fuel rail pressures.

Now turning to FIG. 5, an example routine 500 is shown for adjustingengine operations, including fuel injection, during an engine restartfrom idle-stop conditions, based on whether or not a high pressure fuelpump of the fuel system is degraded.

At 502, engine idle-stop conditions may be confirmed. These may include,for example, verifying that the engine is operating (e.g., carrying outcombustion), the battery state of charge is more than a threshold (e.g.more than 30%), vehicle running speed is within a desired range (e.g.,no more than 30 mph), air conditioning is not desired, enginetemperature is within a selected temperature range, a start has not beenrequested by the vehicle driver, driver requested torque is less than apredetermined threshold value, brake pedal has been pressed, etc. Assuch, any or all of the idle-stop conditions may be met for an idle-stopcondition to be confirmed.

If idle-stop conditions are not met, the method may end. However, if anyor all of the idle-stop conditions are met, then at 504, the controllermay initiate execution of an idle-stop operation and proceed todeactivate the engine. As such, this may include shutting off fueland/or spark to the engine.

Next, at 506, it may be determined if a high pressure fuel pump of thefuel system is degraded. In one example, degradation of the highpressure fuel pump may have been diagnosed during a previous enginedrive cycle.

If the high pressure fuel pump is not degraded, then at 508, during afirst engine shutdown (preceding a first engine restart), the routineincludes shutting down the engine while maintaining one or moretransmission clutches engaged. In comparison, if the high pressure fuelpump is not degraded, then at 510, during a second engine shutdown(preceding a second engine restart), the routine includes shutting downthe engine while maintaining the one or more transmission clutchesdisengaged.

Returning to 508, after shutting down the engine, at 511, restartconditions may be confirmed. These may include, for example, verifyingthat the engine is in idle-stop (e.g., not carrying out combustion), thebattery state of charge is less than a threshold (e.g. less than 30%),vehicle running speed is within a desired range (e.g., less than 30mph), air conditioning is desired, a start has not been requested by thevehicle driver, driver requested torque is more than a predeterminedthreshold value, brake pedal has been released, etc. If restartconditions are not met, then at 532, the engine may then be maintainedin idle-stop until restart conditions are satisfied.

As such, during an engine restart from idle-stop, an exhaust catalystmay be sufficiently warm and active (e.g., a temperature of the exhaustcatalyst may be at or above a light-off temperature). However, there maybe conditions when the exhaust catalyst is not sufficiently warmed.Thus, after confirming restart conditions, at 512, an exhaust catalysttemperature (Tcat) may be estimated and/or measured and it may bedetermined if the exhaust catalyst temperature is at or above athreshold temperature (such as a catalyst light-off temperature). If thecatalyst temperature is above the threshold temperature, then at 514,during a first engine restart from idle-stop when the high pressure fuelpump is not degraded, the routine includes direct injecting fuel asmultiple injections into a first firing cylinder during a compressionstroke (that is, as a split compression injection). In one embodiment,the compression stroke injection may be continued into a first number offiring cylinders. Specifically, during the first engine restart, thedirect injecting may include direct injecting during the compressionstroke for a first larger number of combustion events since the enginerestart. The first number of combustion events may be based at least onthe configuration of the engine. For example, the number of combustionevents may range between Num_cyl/2 to Num_cyl where Num_cyl refers tothe number of cylinders in the engine. As an example, on an I4 engine,the first number of combustion events may vary from 2 to 4. The numberof combustion events over which the multiple compression strokeinjections are performed may also be based on a trade-off between enginerestart robustness relative to exhaust emissions, in particular smokingFor example, the number of compression injection events may be selectedas the number of combustion events required to pump down the intakemanifold to an idle MAP value of ˜35-45 KPa. As such, this assures thatcompression injection will be used while there is a need to use higherspark retard to minimize the engine flare. In some manual transmissionapplications, a single compression injection event can be used if agreater amount of engine flare can be tolerated or if the engine inertiais high enough that spark retard is not required to suppress the flare.

Next, at 515-520, various engine operating parameters may be adjustedbased on the compression injection. Specifically, at 515, during thefirst engine restart, spark timing may be retarded by a first largeramount (e.g., −25 CA deg) while direct injecting fuel in the compressionstroke. At 516, a first, larger alternator load may be applied on theengine until a threshold engine speed (e.g., an idling engine speed) isreached. At 518, an intake air throttle may be maintained, or held,closed (that is, less open) for a number of combustion events during therun-up. By adjusting the various engine operating parameters based onthe compression injection, engine speed overshoot at restart and restartNVH issues may be reduced. Additionally, launch smoothness of thevehicle may be improved.

At 520, the routine further includes not disabling an automatic engineshut-down responsive to idle-stop conditions following the first enginerestart. That is, since the high pressure pump is functional, engineidle-stop operations may be enabled.

As such, the compression stroke injections may be continued until athreshold engine speed is reached (such as an engine idling speed).Thereafter, fuel injection timing may be adjusted based on engineoperating conditions including engine speed and load conditions.

Returning to 512, if the exhaust catalyst temperature at the onset ofthe engine restart is not above the threshold temperature (that is, thecatalyst is not sufficiently warmed), then at 513, the routine includes,during the engine restart from idle-stop, injecting fuel into at least afirst firing cylinder in the intake stroke. From there, the routine mayproceed to 514 and resume compression injection. In one example, thecontroller may inject fuel into the first firing cylinder as a singleintake stroke injection and inject fuel into subsequent firing cylindersas multiple compression stroke injections. In another example, thecontroller may inject fuel into a selected number of firing cylinders(or a selected number of combustion events since the engine restart) asa single intake stroke injection, until the exhaust temperature is at orabove the threshold temperature, and then resume fuel injection asmultiple compression stroke injections until the engine speed is at orabove a threshold engine speed. Then, after the engine speed is at orabove the threshold engine speed (and above the threshold catalysttemperature), fuel injection timing may be adjusted based on engineoperating conditions including engine speed and load conditions.

As such, while injecting fuel in the intake stroke, the various engineoperating parameters (e.g., throttle opening, valve timing, sparktiming, alternator load, etc.) may be adjusted based on the intakestroke injection, rather than the compression stroke injection. Asfurther elaborated below, this may include, during the intake strokeinjection, applying a smaller amount of spark retard, a smaller amountof alternator load, a larger throttle opening, more valve overlap, etc.By injecting fuel in the intake stroke when an exhaust catalyst is notsufficiently warm, more time may be allowed for fuel vaporization andfuel-air charge mixing, reducing engine restart exhaust emissions duringcold catalyst conditions.

Returning to 510, after shutting down the engine, at 521, restartconditions may be confirmed. If restart conditions are not met, then at532, the engine may then be maintained in idle-stop until restartconditions are satisfied.

If restart conditions are confirmed, then at 522, during a second enginerestart from idle-stop, when the high pressure fuel pump is degraded,the routine includes direct injecting fuel as a single injection intothe first cylinder during an intake stroke. In one embodiment, theintake stroke injection may be continued into a second number of firingcylinders. Specifically, during the second engine restart, the directinjecting may include direct injecting during the intake stroke for asecond smaller number of combustion events since the engine restart.

It will be appreciated that while the example of FIG. 5 illustrates thefirst engine restart with multiple compression injections performed overa first larger number of combustion events since the restart and withthe second engine restart with single intake stroke injection performedover a second smaller number of combustion events since the enginerestart, this is not meant to be limiting. In alternate examples, basedon engine operating conditions and the engine configuration, the firstengine restart may include compression injections performed over thesame number of combustion events as the number of combustion events overwhich the intake injections of the second engine restart are performed.Further still, the first engine restart may include compressioninjections performed over a first number of combustion events largerthan the second number of combustion events over which the intakeinjections of the second engine restart are performed.

Next, at 524-530, various engine operating parameters may be adjustedbased on the intake stroke injection. Specifically, at 524, during thesecond engine restart, spark timing may be retarded by a second smalleramount while direct injecting fuel in the intake stroke. As an example,spark timing may be shifted to an absolute value of 10 CA degrees BTDC.At 526, a second, smaller alternator load may be applied on the engineuntil a threshold engine speed (e.g., an idling engine speed) isreached. That is, the alternator load may be minimized until after theengine speed has crossed the target idle speed. At 528, an intake airthrottle may be released so that is it more open for a number ofcombustion events during the run-up. By adjusting the various engineoperating parameters based on the compression injection, engine speedovershoot at restart and restart NVH issues in the absence of afunctional high pressure pump may be reduced. Additionally, launchsmoothness of the vehicle in the presence of a degraded high pressurepump may be improved.

As such, the intake stroke injections may be continued until a thresholdengine speed is reached. For example, until an engine idling speed isreached. Thereafter, fuel injection timing may be adjusted based onengine operating conditions including engine speed and load conditions.

At 530, the routine further includes disabling an automatic engineshut-down responsive to idle-stop conditions following the second enginerestart. That is, since the high pressure pump is degraded, furtherengine idle-stop operations may be disabled. By disabling engineidle-stops, reduced engine startability on subsequent engine restarts,arising from the high pressure pump degradation, can be betteraddressed.

FIG. 6 depicts an example fuel injection timing chart 600 with examplevariations in injection settings for fuel injected in a first firingcylinder during an engine restart in the presence or absence of highpressure fuel pump degradation.

In one example, when operating the engine while the high pressure pumpis functional, fuel may be injected into a first firing cylinder duringthe compression stroke (solid bars) as multiple injections (herein,depicted as two injections of equal amount). An average timing and netamount of the compression stroke injection may be based on engineoperating conditions including engine speed/load conditions, alcoholcontent of the injected fuel, etc. To reduce potential issues associatedwith the increased fuel rail pressure available in the presence of afunctional high pressure fuel pump, such as fuel hitting the cylinderwalls and/or the piston surface, multiple compression injections may beperformed. It will be appreciated that while the depicted exampleillustrates the compression injection as symmetric double compressioninjection, this is not meant to be limiting. In alternate examples, alarger number of injections may be possible which may be arranged to besymmetric or asymmetric. Likewise, a timing between the injections aswell as a time of opening and closing of the fuel injectors may beadjusted based on engine operating conditions (such as an alcoholcontent of the fuel). Herein, injection timing may be retarded into thecompression stroke to take advantage of the compression stroke's highercylinder valve temperature and aircharge temperature, thereby improvingengine restartability.

In another example, when operating the engine while the high pressurepump is degraded, fuel may be injected into the first firing cylinderduring the intake stroke as a single injection (hatched bar). A timingand amount of the intake stroke injection may be based on engineoperating conditions including engine speed/load conditions. Herein,injection timing may be advanced into the intake stroke to use thereduced fuel rail pressure for injecting fuel into the first firingcylinder, thereby improving engine restartability even when the highpressure pump is degraded.

In this way, during an engine restart, when sufficiently high fuel railpressures are not available due to high pressure fuel pump degradation,fuel may be injected into an intake stroke to improve cylindercombustion and engine cranking By continuing intake stroke injectionuntil a threshold engine speed is reached, engine startability can beimproved, and the likelihood of engine stalls due to high pressure pumpdegradation can be reduced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described steps maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be further appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above technology canbe applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types.The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereofSuch claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method of operating an engine, comprising: during an engine coldstart condition, direct injecting fuel into a first firing cylinderduring an intake stroke independent of a state of a high pressure fuelpump coupled to the engine to restart the engine.
 2. The method of claim1, wherein the direct injecting independent of a state of the highpressure fuel pump includes, direct injecting fuel into the first firingcylinder during the intake stroke if the high pressure fuel pump is notdegraded, and direct injecting fuel into the first firing cylinderduring the intake stroke if the high pressure fuel pump is degraded. 3.The method of claim 1, wherein the engine cold start condition includesone or more of an exhaust catalyst temperature being below a thresholdtemperature, and the engine being in an engine-off condition for greaterthan a threshold time.
 4. The method of claim 1, further comprising,continuing direct injecting fuel during an intake stroke for a number ofcombustion events since the engine restart, the number of combustionevents based on whether or not the high pressure fuel pump is degraded.5. The method of claim 4, wherein the continuing direct injecting for anumber of combustion events based on an engine speed includes directinjecting for a number of combustion events until an engine speed is ator above a threshold speed.
 6. The method of claim 5, furthercomprising, while direct injecting fuel during the intake stroke,adjusting an ignition spark timing based on the direct injection.
 7. Themethod of claim 6, further comprising, while direct injecting fuelduring the intake stroke, applying an alternator load on the engine, thealternator load based on one or more of combustion event number, andspeed profile.
 8. The method of claim 1, further comprising, adjustingan intake and/or exhaust valve timing of the first cylinder so that thedirect fuel injection occurs during positive valve overlap.
 9. Themethod of claim 1, wherein the direct injecting during an intake strokeincludes direct injecting fuel as a single injection during the intakestroke, and wherein the direct injecting during a compression strokeincludes direct injecting fuel as multiple injections during thecompression stroke.
 10. A method for an engine, comprising: during afirst engine restart from idle-stop, when a high pressure fuel pump isnot degraded, direct injecting fuel as multiple injections into a firstcylinder during a compression stroke; and during a second engine restartfrom idle-stop, when the high pressure fuel pump is degraded, directinjecting fuel as a single injection into the first cylinder during anintake stroke.
 11. The method of claim 10, wherein during the firstengine restart, the direct injecting includes direct injecting duringthe compression stroke for a first larger number of combustion eventssince the restart, and during the second engine restart, the directinjecting includes direct injecting during the intake stroke for asecond smaller number of combustion events since the restart.
 12. Themethod of claim 10, further comprising, during the first engine restart,retarding spark timing by a first larger amount while direct injectingfuel, and during the second engine restart, retarding spark by a secondsmaller amount while direct injecting fuel.
 13. The method of claim 10,further comprising, during the first engine restart, applying a first,larger alternator load on the engine until a threshold engine speed isreached, and during the second engine restart, applying a second,smaller alternator load on the engine until the threshold engine speedis reached.
 14. The method of claim 10, further comprising, during thefirst engine restart, maintaining an intake throttle open for a numberof combustion events, and during the second engine restart, maintainingthe intake throttle less open for the number of combustion events. 15.The method of claim 10, further comprising, disabling an automaticengine shut-down responsive to idle-stop conditions following the firstengine restart.
 16. The method of claim 10, further comprising, during afirst engine shutdown preceding the first engine restart, shutting downthe engine while maintaining one or more transmission clutches engaged;and during a second engine shutdown preceding the second engine restart,shutting down the engine while maintaining the one or more transmissionclutches disengaged.
 17. An engine system, comprising: an engineconfigured to be selectively deactivated responsive to idle-stopconditions; a fuel injector configured to directly inject fuel into anengine cylinder; a first high pressure fuel and a second low pressurefuel pump configured to deliver fuel from a fuel tank to the injector; acontroller with computer readable instructions for: during an enginerestart from idle-stop, in response to degradation of the first fuelpump, shifting direct fuel injection into a first firing engine cylinderfrom a compression stroke to an intake stroke for a number of combustionevents since the restart.
 18. The system of claim 17, wherein theshifting includes shifting fuel injection from a multiple fuel injectionin the compression stroke to a single fuel injection in the intakestroke
 19. The system of claim 17, wherein the first firing cylinder isa first cylinder to reach TDC upon engine restart.
 20. The system ofclaim 17, further comprising an alternator, wherein the controllerincludes further instructions for applying a reduced alternator load onthe engine during the restart until a threshold speed is reached.